Elastomeric compositions are useful for a variety of abrasion resistant articles such as tire components and shoe components. There is a need to improve the balance between grip properties under a variety of service conditions (traction on dry, wet and winter surfaces) and durability (wear life) of the rubber article. No one elastomer is capable of delivering the desirable balance of properties to date. For example, it is known that cis-polybutadiene (BR) exhibits excellent abrasion resistance (high DIN Abrasion values), but has poor grip. Likewise, polymers such as butadiene-acrylonitrile-styrene rubber (SNBR) exhibit desirable wet traction properties (based on Tangent Delta (G″/G′) values at 0° C.), but low abrasion resistance and low winter traction (based on Tangent Delta (G″/G′) values at −30° C.). Further, brominated poly(isobutylene-co-p-methylstyrene) (BIMS) polymers are known to exhibit good traction (based on the Tangent Delta values), but poor abrasion resistance.
A combination of elastomers can be used to achieve a balance of properties for abrasion resistant articles. However, this combination must be achieved while maintaining other desirable properties, such as maintaining grip and abrasion resistance when combined with fillers such as silica, which tend to decrease abrasion resistance. One method of achieving an optimal balance of properties is to optimize the curatives used to cure the elastomeric composition. While the use of metal oxide and sulfur is common, the compositions can be further optimized by the appropriate choice of other curatives. Thiourea curatives are one example of a general class of curatives that have been disclosed as a possible additive to certain curable compositions, such as, for example, in U.S. Pat. Nos. 5,684,007; 6,013,218, 6,334,919, and H1,922. However, it is unclear what type of “thiourea” may be useful, and the amount that is optimal. Further, the utility of thioureas in compositions including BIMS as the only elastomer, or in combination with other elastomers, has not been described.
Thus, there is a need to find the optimal balance of curative with a balance of various elastomers in order to achieve a desired cured composition having both desirable traction properties with desirable abrasion resistance properties. The present invention is directed towards such a need.
Other background references include WO 92/01575, EP 0 857 761, and U.S. Pat. No. 5,594,073.